Santa Maria

Guatemala

14.757°N, 91.552°W; summit elev. 3745 m

All times are local (unless otherwise noted)

Seismometers near the volcano detected rates of rockfalls and explosions that were markedly lower in January and February (<10 explosions/day) than in most of 1990 (20-100 explosions/day; 15:11). The 8-9 February observations were from the newly constructed Santiaguito Volcano Observatory (figure 19) [see BGVN 15:11 for a description of the Observatory, including material originally in BGVN 16:02]. More than 20 pyroclastic flows and lateral blasts were observed between April and early December 1990, but none have been reported since then. SO2 emission measured by COSPEC (from 3.4 km S of the dome's Caliente vent) was 35 ± 7 t/d on 8 February and 62 ± 24 t/d the next day, similar to the 48 ± 15 t/d of 22 February 1990.

Figure 19. Santiaguito Dome complex (left background) with a small plume emerging from Caliente Vent at left-center. Santa María volcano is at center background, partially obscured by clouds. At right foreground is the new Santiaguito Volcano Observatory, at Finca El Faro, [7] km S of the dome.

Geologic Background. Symmetrical, forest-covered Santa María volcano is one of the most prominent of a chain of large stratovolcanoes that rises dramatically above the Pacific coastal plain of Guatemala. The stratovolcano has a sharp-topped, conical profile that is cut on the SW flank by a 1.5-km-wide crater. The oval-shaped crater extends from just below the summit to the lower flank and was formed during a catastrophic eruption in 1902. The renowned Plinian eruption of 1902 that devastated much of SW Guatemala followed a long repose period after construction of the large basaltic-andesite stratovolcano. The massive dacitic Santiaguito lava-dome complex has been growing at the base of the 1902 crater since 1922. Compound dome growth at Santiaguito has occurred episodically from four westward-younging vents, the most recent of which is Caliente. Dome growth has been accompanied by almost continuous minor explosions, with periodic lava extrusion, larger explosions, pyroclastic flows, and lahars.